Conventionally, a switching regulator is used for generating a plurality of mutually insulated DC power sources from one DC power source. For example, a power supply of an inverter device drives an AC servomotor of an automated guided vehicle (AGV) by a battery source, as the power supply, based upon the factors of weight, conversion efficiency, and space occupied.
In this conventional switching regulator, one switching control circuit and one switching transistor are used to generate a chopped voltage. The chopped voltage is applied to one power transformer, and a required DC power source is then generated.
Note, an AC servomotor is generally used as a travelling motor or a lifting motor of the AGV, since it does not require a brush and has maintenance advantages. To drive and control the above AC servomotor, in addition to the main power source for a main control circuit, a driving power source, insulated from the main power source, is required.
This driving power source is a power source for a driver circuit which amplifies a signal from a control circuit and drives high capacity power transistors, so that the AC servomotor is supplied with the controlled power source. The driving power sources are not only insulated from the control circuit, but also insulated from one another. For example, where one AC servomotor is driven by a three phase alternating current, six pairs of mutually insulated driving power sources are required for six driving transistors.
As mentioned above, a conventional switching regulator uses one switching control circuit and one switching transistor, and a chopped voltage is applied to one transformer, so that the power supply generates a required DC power source. Therefore, for example, where one AC servomotor is driven by a three phase alternating current, six pairs of mutually insulated driving power sources are required, and thus many secondary windings for the six pairs of driving power sources must be wound on the one transformer.
When a required number of secondary windings of the driving power sources are wound on one transformer, however, the weight of the transformer is increased and a printed substrate on which the transformer is mounted is liable to be damaged. Furthermore, the number of pins of the transformer is increased and the external form of the transformer becomes large. Additionally, many secondary windings are wound on the one transformer and many connecting pins are concentrated, so that many power lines must be led from the transformer position to other positions supplying the power sources. Further, so many connecting pins of the transformer are fixed on the printed substrate that the printed circuits become complex, and especially when a power source voltage is very high, a distance between the printed circuits must be enlarged to avoid a spark discharge therebetween. Consequently, the printed substrate must be enlarged and it is difficult to improve a packing density of the device.